Not Applicable.
1. Field of the Invention
This invention relates to a cooling fan of a rotary electromechanical machine. More particularly, the invention is directed to retaining a cooling fan on a shaft of an alternator assembly.
2. Description of the Related Art
One type of known electromechanical machine is an alternator comprising an alternator housing, a stator, rotor shaft, two iron pole pieces, one or more cooling fans, electrodes, and a rotor coil. A vast majority of all vehicles driven today use front-end accessory drive alternators that contain Lundell type rotors. The Lundell type rotor is used to generate the magnetic field within an alternator. The magnetic field of the rotor is generated when the field coil of the rotor, made up of insulated copper wire wrapped around an electrically insulated bobbin that surrounds a steel hub, is energized and a current flows through the wire. The rotor in conjunction with stator generates electrical power for the various components utilized by the automobile. Since the alternator is driven by the engine, it has a substantial impact on fuel economy. It is therefore critical and strategic to alternator and automobile manufacturers to improve alternator efficiency for increasing the fuel economy. In order to improve the efficiency of any electrical machine it is necessary to reduce the losses within the machine. The losses can generally be categorized as either mechanical, electrical, or core. Losses in the alternator are dissipated as heat generated within the machine. It is critical to the alternator to improve the heat dissipation to allow for cooler operation and improved efficiency. One such method to increase heat dissipation is to provide one or more cooling fans within the alternator to create a cooling airflow along the rotor, the stator, and/or a rectifier.
Cooling fans are typically welded to an end (e.g. front or back face) of the rotor pole core surfaces. It is well known in the industry that a robust attachment of the fans to the pole core is becoming an increasing difficult task in light of increases in operating speeds of the rotor. Vehicle maximum engine RPM""s continue to increase, and the demand for increased electrical power leads to smaller pulley sizes on alternators to facilitate rotating the rotor at higher RPM""s when at engine.
Currently, internal alternator fans are generally resistance or laser welded onto the end surface of the pole core which consists of low carbon steel. This traditional method of attaching the cooling fan leads to a number of disadvantages especially if the process is performed by machine automation. Such disadvantages include expensive manufacturing equipment, expensive and labor intensive maintenance, significant downtime, and difficulties in controlling the welding quality in a production environment. Resistance welders require frequent maintenance to replace copper electrodes and realignment of fixtures. Laser welders often require lens and shield replacement along with downtime related to changing laser bulbs as part of regular maintenance. Furthermore, welding operations can produce a significant amount of scrap due to incorrect welds or as a result of in-production process validation testing of the weld strength which is usually a destructive test.
The present invention has the advantage of retaining a cooling fan about a shaft of a dynamo-electric machine without having to weld the cooling fan to an end of a pole core.
In one aspect of the invention, a method is performed for attaching a fan to a rotor assembly for a dynamo-electric machine. A shaft is provided for being mounted within a housing of the dynamo-electric machine. The shaft includes an integral shoulder portion for creating an abutment surface. A fan which includes a fan base and a plurality of fan blades protruding from the fan base is mounted on the shaft. The fan base has a central bore wherein the inner circumference of the fan base along the central bore is juxtaposed to the abutment surface. A pair of pole cores is mounted axially along the shaft toward the shoulder portion so as to clamp the fan between a respective end of the pole cores and the abutment surface.